Shielded ignition cable



195G L. M. WRTTLENGER 295299795 SHIELDED IGNITION CABLE Filed March 21,1945 mph-z! case encz'osz'ng zyrzzizon disirzbuior 9 gglferv zz'ndl a zz 1022 6265;555:207; 42 Mdgrre 0 or genertor F1 2 I 36 44, 27 1 l 2: 29I 30 3/ Z5 1; j 32 4,5 j:

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I we; Hi5 ATTORNEYS Patented Aug. 29, 19

52ers SHIELDED IGNITION CABLE Leonard M. Wittlinger, Flint, Mich.,assignorto General Motors Corporation, Detroit, Mich., a

corporation of Delaware V Application March 21, 1945, Serial No..583,967

This invention relates to the shielding of ignition cables for theignition system of internal combustion engines so that their ffect uponradio apparatus in proximity to the ignition system is reduced orentirely eliminated.

It is well known that in the ignition system for an internal combustionengine, due to the periodic breaking and making of the ignition circuit,the high tension circuit and the spark plug discharge sets up a fieldand lectromagnetic waves are produced in the atmosphere surrounding thesystem to such an extent as to create considerable interference with theproper reception in radio communication in apparatus that is in thevicinity of the ignition system. The high tension ignition system forinternal combustion engines pI'O-r duces disturbances that are soviolent that good radio reception is practically impossible. This isespecially true in aircraft engines. Therefore, because of theseinterferences it is imperative that the ignition cables be properlyshielded and grounded for the successful operation of the radioequipment.

Heretofore it has been the practice in conventional ignition systems,particularly aircraft ignition systems, to enclose the ignition cablesin a rigid or combination of rigid and air tight flexible tubing in ordr to eliminate ignition interference upon the radio receiving apparatus.In the flexible portion of shielding system it was the practice to use asoldered spiral bellows or a continuous convolution type bellows inorder to have an air tight system. Therefore it is one of the objects ofthe present invention to provide a flexible cable that is structurallystronger than the bellows type and on that need not be air tight.

In order to shield effectively extraneous apparatus, namely, radioapparatus, against violent electrical disturbances caused by ignitionsystem of an internal combustion engine, it is essential that conductorsof the ignition system be completely enclosed by a plurality of metallicsurfaces; and that enclosing metallic surfaces be electrically connectedtogether at the ends and grounded. Therefore, it is another object ofthe present invention to provide an eflcient radio shield for enclosingthe ignition conductor which shield shall comprise an inner shield, oflow resistance and an outer shield of high resistance and connecting theshields together and to ground. By this arrangement the lower frequencycurrents divide in proportion to the resistance of the low resistanceinner shield and the higher resistance outer shield. In the case of theultra high frequencies they tend to travel 5 Claims. (Cl. 174-36) thecylinder head 20.

on the surface of a conductor and therefore would be on the innersurface of the low resistance inner shield and be out of phase with itscorresponding current in the main conductor and cancel the fields. Anystray field would then be absorbed by the higher resistance steel outershield.

Further objects and advantages of the present invention will be apparentfrom th following description reference being had to the accompanyingdrawings wherein a preferred embodiment of the present invention isclearly shown.

In the drawings:

Fig. 1 is a side elevation, partly broken away and partly in section ofan ignition conductor embodying the present invention.

Fig. 2 is a fragmentary view showing a modified form of the presentinvention shown in Fig. 1. but showing concentric conductors.

Referring to Fig. 1, 20 designates a fragment of a cylinder headsupporting a spark plug 2| having a base 22. Disposed around the base ofthe plug is a metal tubular member 23 having at its bottom an internalflange 24 adapted to seat on The member 23 is rigidly secured to thecylinder head by the base 22 of the plug when the plug is affixed to thecylinder head. The top of the tubular member 23 terminates in a screwfitting or nipple 25 for the attachment of a coupling member 26 having abore 21 for receiving a cabl 28. Screwed in the coupling 26 is a tubularmember 29 of insulation having a bore in alignment with the bore 21. Thebores 21, 29 receive one end of the cable 28 having a conductor 29awhich may be a plurality Of copper strands. The lower end of the bore 30is closed by a contact member 3i having a pointed portion which isforced between the flexible strands 29a. The lower side of the contactmember 3! has affixed thereto in any suitable manner a spring 32 formaking contact engagement with the central electrode 33 of the sparkplug 22 l.

The upper end of the coupling member 26 in this instance is providedwith a threaded portion 35 the end of which has a surface against whichone end of a flanged coupling member 3% rests. The coupling member 36 isprovided with a skirt 3? to which is attached one end of the shieldedcable comprising one form of the present inven tion, as shown in Fig. 1.The shielded cable includesthe conductor 25a covered with suitableinsulating material. It is desirable that the core have a minimum amountof inductance. About the insulation of the cable 2% a flexible metallicshield ill, preferably of braided copper wire, is

3 wound. It is pointed out that the braided metallic shield 40 may bemade of any suitable metal, for instance aluminum or other metalhaving aresistance equal to or appreciably lower than the copper conductorstrands forming the core c. This shield of low resistance will bereferred to hereinafter as the inner shield." About the inner shield asheath of insulation 4| is provided, this sheath isn't necessary fromthe radio stand-. point. The purpose of the insulation between the twoshields, as shown, is purely a. matter of preventing abrasion betweenthe two shields or to exclude any moisture or electrolytic actionbetween .the dissimilar metals. On the outside of the insulated sheath4| a flexible metallic shield 42 of the stranded wire is provided andsaid .4 in the case 58. The ferrule ll could be afllxed to the case 56by soldering or spot welding.

In Fig. 2 the modified form of the invention two concentric conductors65 and 46 are used, the conductor 65 being substantially straight whilethe conductor 46 may be a woven or spiral form. It is to be understoodthat more than two conductors may be used so long as the conductors areinsulated from each other and from ground. It is to be understood thatthe ends of the conductor 68 will be straightened out so that same canbe easily attached to suitable terminals,.,not

shield has an iron or steel base. This latter shield 42 has a higherresistance than the inner shield" 40 and will be known hereinafter asthe outer shield. It is pointed out that the arrangement of lowresistance shield 40 and the higher resistance shield 42 may be reversedif desired.

One end of the flexible shielded cable 28 is at tached to the couplingmember 38. The flexible shields 40 and 4| terminate short of the ends ofthe cable 28 to allow the cable to extend through the bore 21 of themember and, into the bore 30 of the member 25. The inner shield contactsthe inner surface of the skirt 31 while the outer shield 42 contacts theouter surface of the skirt 31, by soldering or other suitable means, andthereby electrically connecting the shields 40 and 42 together. Theinsulation 4| terminates short of the ends of the shields 40 and 42 andabuts the upper end of the skirt 3'! as shown in Fig. 1. A sleeve orferrule 43 of metal is attached to the outer shield" 42 by swaging orsoldering. The upper end of the coupling member 26 is provided with aplane surface against which the flange portion of the coupling member 36rests. A nut 45 is adapted to engage a flange provided by the ferrule 43and press the flange against the flange of the coupling member 36 whichin turn is pressed against the plane surface of the threaded portion 35,and thereby form a tight joint and ground connection. If desired, inorder to get a high pressure unit pressure metal to metal contact theflange of the coupling member 36 could be formed with a V-shapedprojection or other suitable sharp cornered means which will pressagainst the plane surface of the part 35.

The other ends of the shields 40 and 42 are connected together by aferrule having a bore of step formation to provide an internal shoulder52. The ends of the shields 40 and 42 terminate short of the end of thecable 28 in a manner that the outer shield 42 and the insulation 4! abutthe shoulder 52 while the outer shield 42 contacts the interior of theferrule as at 53. The inner shield 40 extends into and contacts theferrule within the reduced portion of the bore. Thus, the inner andouter shields 40, 42 are electrically connected together by swaging,soldering or other suitable means. The ferrule is provided with anxternal flange 55 which abuts a metal case 56 when the end 51 of theferrule 50 extends through an aperture 59 provided by the case 56. Theend 51 is shown as suitably recessed and riveted over as at 60 to holdsecurely the ferrule to the case 56 to provide a ground connection. Itis to be understood that other suitable means could be used to attachthe ferrule 50 to the metal case 56- to provid the ground connection.For example, the end 51 could be provided with threads and screwed intoan appropriate aperture shown. A sheath 61 of insulation separates theconductors. Both conductors 65, 66 extend beyond the ends of twometallic shields 4B, 42. Since these shields 40, 42 correspond to theinner and outer shields described in Fig. 1 they are given the samereference character and therefore need not be described in detail. Thetwo shields 40 and 42 are connected electrically in the manner asdescribed from the construction shown in Fig. 1. The ferruleconstruction shown in Fig. 2 is substantially the same as ferrule 50with the exception of the end which is attached to the metal case isprovided with threads 68.

It is pointed out here that the metals specified for the inner and outershields 40, 42 are preferred, but it is to be understood that othermetals could be utilized producing equivalent results. If desired, thearrangement of the shields of low and of higher resistance may bereversed.

As set forth heretofore the inner and outer shields 40, 42 terminateshort of the cable 28. By this arrangement the cable extended ends canbe easily attached to terminals one end to a terminal of a distributor(not shown) enclosed within the casing 56 while the other end is forcedover the pointed projection of the contact 3| shown in Fig. 1.

It will be observed that in the foregoing described structure that bothends of the inner and outer shields 40, 42 are electrically connectedtogether and grounded. This arrangement is of great value in eliminatingignition interference upon the radio receiving system. It has been foundthat by grounding the shields at both ends a much more effective shieldis provided and that the need for shielding the conductor for the radioequipment is unnecessary so far as ignition radiation is concerned.

It will also be observed that the inner and outer metallic shields 40,42 are spaced from each other by the sheath 4| of insulating material.It is pointed out here that this sheath is not necessary from thestandpoint of suppress.- ing radio interference. It has been found thatwhen the outer shield 42 of steel braided wire was directly in contactwith the inner shield of copper the radio system is quiet. As set forthheretofore, the purpose of the sheath of insulating material for spacingthe inner and outer shield would be to prevent abrasion between the twoshields, to exclude moisture and prevent electrolytic action between thedifferent metals.

While the embodiment of the present invention as herein disclosed,constitutes a preferred form, it is to be understood that other formsmight be adopted, all coming within the scope of the claims whichfollow.

What is claimed is as follows:

1. An ignition cable assembly including a central metallic conductorsurrounded by a covering of yieldable insulating material; an innerflexible metallic shield surrounding and fitting against the insulatingmaterial; an outer flexible shield surrounding the inner shield, both ofthe shields terminating short of the opposite ends of the cable, one ofsaid shields having a higher resistance than the other; a tubularmetallic member supported on each end of the cable and fitting over theinner shield and engaging the outer shield to connect electrically bothshields together, said tubular member engaging the shields withsufiicient force to anchor the inner shield to the insulating materialand also to prevent longitudinal movement of the metallic members andthe shields relative to the insulating material, said members operableto ground the shields when assembled in one ignition circuit.

2. An ignition cable assembly including a central metallic conductorsurrounded by a. covering of yieldable insulating material; an innerflex ible metallic shield surrounding and fitting against the insulatingmaterial; an outer flexible shield surrounding the inner shield,insulating means disposed between the shields to prevent abrasionbetween the shield; a tubular metallic member supported on each end ofthe cable and fitting over the inner shield and engaging the outershield to connect electrically both shields together, said tubularmember engaging the shields with suflicient force to anchor the innershield to the insulating material and also to prevent longitudlnalmovement of the metallic members and the shields relative to theinsulating material, said members operable to ground the shields whenassembled in one ignition circuit.

3. An ignition cable assembly including a central metallic conductorsurrounded by a covering of yieldable insulating material; an innerflexible metallic shield surrounding and fitting against the insulatingmaterial; an outer flexible shield surrounding the inner shield, saidshields being of less length than the cable; a pair of bendable sleevesslidably mounted on the cable, said sleeve having a portion fittingagainst the inner shield and another portion engaging the outer shieldto connect electrically the shields together said sleeves adapted to beswaged to anchor the inner shield to the cable to retain the sleeves andthe shields in immovable relation to the cable.

4. A means for shielding a flexible cable, said means comprising a pairof bendable metal sleeves slidably mounted on the cable, each of saidsleeves having an internal diameter larger than the cross dimension ofthe cable; a pair of concentric flexible shields disposed on said cable,said shields being of less length than the flexible cable with one ofsaid shields having a higher resistance than the other, the sleeves andshields being adjustable along the cable the ends of the shieldsengaging different portions of sleeve, said sleeves being adapted to beswaged against the shields and causing the inner shield to be im--pressed into the cable to retain the sleeves and the shields in fixedrelation on the cable.

5. An ignition cable assembly comprising, a plurality of concentricconductors insulated from each other within a flexible body of yieldableinsulating material; an inner flexible metallic shield about the body;an outer flexible metallic shield about the inner shield, both of theshields being of less length than the flexible body; one of said shieldshaving a high resistance while the other shield has a lower resistance,insulating means disposed between the shields to prevent abrasionbetween the shields a metallic sleeve slidable on the body at each endof the shields and being adapted to engage both shields to connectelectrically both shields together, said sleeve being adapted to bedeformed against the shields and causing the inner shield to be embeddedin the body to retain the sleeves and the shield in immovable relationto the body whereby said sleeves are capable of grounding the shieldswhen assembled in an ignition circuit.

LEONARD M. WI'I'IJLINGER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 809,313 Lougee Jan. 9, 19062,047,152 Mitchell July 7, 1936 2,082,800 Holliday June 8, 19372,105,791 Mascuch Jan. 18, 1938 2,226,479 Pupp Dec. 24, 1940 2,234,579Robertson Mar. 11, 1941 2,362,034 stahl Nov. 7, 1944

